For tanks and other receptacles or reservoirs containing liquids which must be held at a substantially constant temperature or must be protected from the incursion of heat or cold or from the loss of heat and cold, it is known to provide on the vessel a layer of thermally insulating material which can be in the form of discrete thermally insulating elements which are so applied to the outer wall of the vessel as to fit closely therearound.
This has the disadvantage that the individual elements must be designed precisely for the particular vessel to which they are to be applied and hence an wide variety of different elements with various dimensions and sizes must be stocked.